Filter for radio sets



Jan.5, 1937. F. KELLER FILTER FOR RADIO SETS Filed March 24, 1952 Zneiyer In/enfor Patented Jan- 1. 7

UN ITED STATES PATENT OFFICE I J f I p 2,066,690

FILTER. FOR RADIO SETS Felix Keller, Frankfort-on-the-Main, Germany Application March 24, 1932, Serial No. 600,992 1 x p 2Claims. (01. 250-20) The present invention relates to a filter for eliminating-local or interfering broadcast stations. It consists of a separate unit to be inserted into the *c'onnections'* to the antenna and the offs of the coils. The conductive parts of switch 5 are denoted by the numerals 25, 26, 21.

The first lead-off of the coil 8 is connected through the switch 5 and contact 26 with one "5 earth respectively or a radio receiver, and will pole of the variable condenser 4 and to the aerial '5 completely eliminate interference with local a; the second lead-01f goes to the same pole of broadcasting stations 'or with stations, the wave the condenser 4 through the switch 5 and conlength of'which differs but slightly from that to tact 25; the third lead-off goes to the contactbe received, and willflnevertheless allow clear, member l0, and the fourth to the contact-memloud,andeasy reception of the station desired. ber I l; the other pole of the variable condenser 0 The principal idea of the invention consists 4 is connected to the contact-member 9, one pole in inserting between antenna and receiver two of the condenser 2, and contact-member H; the series-connected oscillation circuits which are other pole of the condenser 2 leads to contactcoupled with each other conductively and, prefmember I4 and to terminal I) and thereby to the erably, also inductively and in coupling said ciraerial terminal A of the receiver. The first lead- 15 cuits inductively with a third separate oscilla off of the coil 6 leads to contact-member IS, the tion circuit, which contains a variable capacity second to contact-member l2, the third to Hi, and is inserted into the earth-connection of the and the fourth to contact-member I3. The coil receiver. 1 has only three lead-offs: the first goes to the The coils with their various lead-offs, in comcontact-member 2D, the second to 2|, and the 20 bination with variable condensers of say 250 and third to 22; the condenser 3 is connected on one 500 cm. capacity each (0.00025 and 0.0005 mfd. side with the contact-member 23 and the groundeach) and a number of binding-posts wired as ing of the set through c, and on the other side here described, represent a combination of filters with the contact-member 24 and the ground of 25 with highly remarkable efficiency. It isa feature the filter through d. The connecter is used 25 of the invention that a variable condenser couto connect as desired the group of contact-memple'd with each coil, and a number of lead-offs bers 9, l0, and II. The connecters I8 and I9 led to a suitably located switch, allow the numform connections among the contact-members ber of windings and the inductance of each coil l2, I3, l4, l5, l6, and I1, while the connecters 28 30 to be so set as to clearly obtain the desired wave and 29 form connections among the contact- 30 length in the radio frequency stage of the remembers 20, 2|, 22, 23, and 24. The variable ceiver. condensers 2, 3, and 4 are used to further tune On the accompanying drawings, the invention the filter. is shown as an example: more especially Fig. 1 The mode of operation of the filter device, as

illustrates one practical embodiment of the inset forth, is the following, although the user would 5 vention, whereas Fig. 2 shows in a more diagramnot be limited to the advice given herewith by way matical manner the electrical connections which of example. After the filter set being inserted may be employed. in the antenna circuit A-a and the ground cona is the terminal for the aerial, b is connected nection E-G respectively, as shown in Fig. 2,

with the aerial terminal of the receiver and c the lever 21 of switch 5 is set to touch the con- 4 with the ground terminal of the receiver, while (1 tact 26, the connection 30 is set to connect the is the terminal for the grounding of the filter contact-members 9 and H, similarly connection arrangement. In a container I are contained the i9 is set to connect contact-members l5 and I1, coils 6, l, and 8, made of bakelite tubing or any connection IE to connect contact-members I3 other suitable insulating material, being about 5 and I4, connection 28 to connect contact-mem- 45 centimeters in diameter and wound with about bers 22 and 24 and connection 29 to connect con- 60 turns each of enameled wire of about 0.4 tact-members 20 and 23. The three variable millimeter in diameter. The variable condensers condensers 2, 3, 4 are turned so as to obtain their 2, 3, and 4, as well as the switch 5 are operated zero position. Now the receiver is handled in the from outside the container. The contact-memusual manner and tuned by its own tuning means 50 bers 9, l0, ll, l2, l3, l4, l5, IS, IT, 20, 2|, 22, 23, to that wave length that is intended to be elimiand 24 representing the several lead-offs of the nated. After this the three condensers 2, 3, 4 coils can be connected by means of the connecters (preferably first the condensers 2 and 4 and l8, I9, 28, 29 and 30, so that the variable conafterwards condenser 3) are operated in a well densers can be connected with the several leadknown manner, until the reception of the sta- 55 tion to which the receiver had been tuned, is

totally eliminated. In case the operation of condensers 2, 3, 4 is not quite sufficient for that purpose, one or more of the variable connections 21, 30, I8, I9, 28, 29 respectively may be used at random and by so doing it will be found, by what change of their respective position in regard to their original position the best effect is obtained. Now the receiver may be tuned by its own tuning means to any desired frequency, especially to that differing but slightly from that which is eliminated. Of course it is difiicult to say to which frequency the oscillation circuits containing condenser 4 and coil 8, condenser 2 and coil 6, condenser 3 and coil 1 respectively are tuned or are to be tuned. But in fact there is no need for special advice of that kind, since the users of radio receivers and especially those skilled in the art as a rule do not know either, to what frequency the receiver is to be tuned for receiving a certain station, but they are accustomed to operate the different switches and handles of the receiver by way of trial, until the best reception possible of the desired station is obtained.

The scheme given in Fig. 2 is in substantial conformity with the showing of Fig. 1. The only difference consists in that the contact-member 2| is for the sake of better clearness divided in two contact-members 2| and 2! which are conductively connected with each other. No special advice is to be given for the employment of the device shown in Fig. 2 as everything said in connection with Fig. 1 applies equally to Fig. 2.

I claim:

1. A filter device to be used in connection with wireless receiving stations which comprise a receiver, antenna and ground connection in order to eliminate local broadcast stations and to separate from each other interfering stations with but slightly different wave lengths, consisting of a set of two series-connected oscillationcircuits coupled with each other conductively and of a third and separate oscillation circuit, which is coupled inductively with at least one of the said series-connected oscillation circuits and contains a variable capacitance, the said set of two oscillation circuits havingconnection on one side to the antenna and on the other side to the aerial terminal of the receiver, but the said third and separate oscillation circuit having connections on the one side to the ground connection of the receiver and on the other side to the ground.

2. A filter device accordin :to the preceding claim, characterized by oscillation circuits com.- prising each a condenser, a coil, connecting leads and variable connecters between condenser and coil, the said coils being provided with---tappings adapted to be alternatively connected by the said variable connecters with the leads leading to the respective condenser in such a way as may be required to tune the said oscillation circuits'ton 0 desired frequency.

FELIX KE 

